Photoflash lamp with primer



April 4, 19 67 W- SCHILLING ETAL PHOTOFLASH LAMP WITH PRIMER Filed March 3, 1965 FIGJ WERNER SCHILLING HANS REIBER REINHARD GORL I |%vE TORS BY AT T NE FIG. 2

United States iPatent @filice 3,312,085 Patented Apr. 4, 1967 3,312,085 PHUTOFLAdl-l LAMP WITH PRIMER Werner Schilling, Heidenheim (Brena), and Hans Reiher and Reinhard Giirl, Augsburg, Germany, assignors to Patent-Treuhand-Gesellschaft fiir Electrische Gluhlampen m.h.I-I., Munich, Germany Filed Mar. 3, 1965, Ser. No. 437,638 Claims priority, application Germany, Mar. 5, 196 3, P 33,765 5 Claims. (Cl. 67-31) This invention relates to a photofiash lamp and more particularly to an ignition means for finely shredded combustible material and oxygen in a hermetically sealed envelope.

In case of heretofore generally used photoflash lamps, the ignition means consists of two current in-leads extending into the bulb or envelope and therein connected by a filament proximate to a primer containing easily i gnitable and an oxidizing agent. For the purpose of ignition, a voltage source is connected to the filament by way of said in-leads. The current impulse flowing through the filament causes the latter to flash whereby the primer ignites and initiates the combustion in the lamp. In case of the usual D.C. ignition, a current is obtained by way of a condenser, for instance of 100 to 200 ,uf., charged from a battery rated at about 15-22 volts. For the purpose of igniting the lamp, the condenser is discharged across the filament. The filament must be very thin to respond to being heated to incandescence by means of the available electric energy. Filaments having diameters of 16.2 mm. to 16.6 m. have proved favorable. The electric resistance must be very low and acceptably amounts to about 0.5 ohm. Mounting of such a small low resistance filament is, however, very difiicult in manufacture. The filament is only about 2 mm. long, and even small changes in length or any changes in the contact resistance from the filament to the current in-leads, will bring about considerable differences from the nominal resistance. If this ignition means is used, inclusive of the low voltage of 15 to 22 volts, a very good contact between the lamp base and the flash gun socket is required. This latter requirement makes additional expenditure necessary by the lamp manufacturer, as well as by the socket manufacturer in provision of highly eflicient lamp contacts or contact arrangements with scraping engagement, for instance, nickel contacts.

To overcome these drawbacks, an ignition means has heretofore been developed operating with high tension utilizing in a photofiash lamp two current in-leads with an ignition material applied thereto so that the ignition spark jumps over to the filling gas whereby the ignition material is brought to reaction.

Another high tension ignition means is known in which the current in-leads carry a non-conducting coating and in which the primer is provided on this coating. The ignition spark breaks down this non-conductive coating and the heat developed as a result of the break-down ignites the primer.

These prior art photoflash lamps without filaments re quire ignition devices producing voltages of much more than 1000 volts whereby energy consumption is very high because the energy contained in the spark contributes for a very brief time interval to heating the ignition mass. In sparking over in gases or in break-downs through solid bodies, the greatest part of the spark energy is absorbed by that gas or body. The very high electrical tensions required with the aforesaid ignition means as well as the high energy consumption, make it necessary to provide ignition devices which have volume and weight much higher than with the heretofore first mentioned ignition means consisting of filament and primers applied to the current in-leads.

by a highly resistive primer.

It is an object of the present invention to provide an ignition means in which the aforesaid drawbacks of the filament method as well as the drawbacks of the high tension spark method are overcome.

Experiments to heat the primer containing finely divided combustible metallic powder and] dielectric binder by direct current passage until chemical reaction begins,

showed the surprising, and at first inexplicable, result in view of the high resistance of the primer of much more than megohms, that with a voltage surge of about 100 volts the primer comes to ignition and energy consumption is not only much lower than the high tension method, but is also lower than with the filament method.

According to the present invention a photofiash lamp is provided having a hermetically sealed bulb or envelope filled with finely shredded combustible material and oxygen. Two current in-leads extend into the bulb and carry the ignition mass, characterized by the fact that both of the current in-leads in the lamp are connected through a primer of ignition mass containing finely divided easily combustible metal and dielectric binder, and wherein the primer is in direct contact with the electrical resistance of the primer functioning within the range below 20 volts, amounting to one megohm or more. The ignition means consequently consists only of the two current in-leads with electrically conductive surfaces bridged No filament is provided bridging the current in-leads.

The definition of electrically conductive surface shall be understood as meaning that there is not provided between current in-lead and ignition mass any insulating coating to be broken down by an ignition spark. A slightly oxidized surface of the filament as it is generally found on most base metals and which causes no considerable voltage drop when the ignition current impulse passes,

shall also be considered as electrically conductive surfaces in the aforesaid sense.

If the ignition voltage applied to the primer is increased from zero continuously by about 10 volts/sec, then ignition is initiated, as an average, at about 70 volts. On impulse-like application of voltage, the average amount of voltage required for ignition of the primer is about 50 volts.

If the direct voltage applied to the primer is slowly increased in the aforesaid manner prior to effecting the ignition, then there may be observed at 30 to 60 volts a stepwise decrease of the originally high resistance of more than one megohm by more than one order of magnitude. In repeating the experiment, this new low resistance is substantially maintained in decreasing the voltage, thereby exhibiting irreversible increase of conductivity. The primer has varied electrically very much. For the purpose of igniting this primer, a much higher electric ignition energy is required.

Checking of the phenomenon has shown that this ignition mechanism is quite diiferent from the mechanisms known hitherto. The structure of the primer consisting of metallic powder and a dielectric binder, and, preferably, also an oxidizing means, constitutes in electrical respect a pile, interlinked longitudinally and transversely, of very small spark gaps or condensers and resistances of different values lying in electrical parallel thereto and in series. Thereby the conductive coatings of the condensers are produced substantially by the metallic particles, and the dielectric is produced by the binder and perhaps by the oxide coating of the metallic powder. If the voltage lying on the ignition system is slowly increased, then breakdowns occur in the range between 30 and 60 volts on different condensers of the meshed network, because the binder is probably destroyed in place at some locavelopment of one or several current paths through the primer results, by which the irreversible increase of conductivity may be explained. Since, however, the partial breakdowns follow temporarily one after the other, the heat released thereby may flow off and does not suffice to initiate the ignition process. If, however, a voltage of about 50 volts is applied suddenly, then the breakdown of so many partial condensers occurs practically simultaneously and results in the heat energy released thereby accumulating and bringing about temperatures which are sufficient for initiating the ignition reaction. The heat released in the micro spark gaps through sparking must, consequently, lead to an adiabatic heating of the particles to be brought chemically to reaction.

The above-mentioned initial resistance of the primer amounting to 100 megohms or more is, therefore, the resistance which is measured before the stepwise decrease of the resistance observed in the range of approximately 30 volts occurs. This resistance may be ascertained with greatest safety if voltages below 20 volts are taken for its measurement.

It has been found that primers with much lower initial resistance than one megohm cannot be brought to ignition with an equal amount of energy. This result is easy to understand if the above described ignition mechanism can be assumed. With the primers having such a low resistance, the resistance lying in parallel with the micro spark gap is too low, and that means too great a part of the current passing through the primer heats up these resistances and withdraws energy from the micro spark gap.

The desired conductivity and the required structure of the primer may be obtained by the choice of the binder, by the precentage of the binder to the entire primer, and/ or by means of grain size and grain size distribution of the finely divided metal of the primer.

The finely divided metal consists preferably of zirconium powder with grain sizes between 0.5 ,um. and m. whereby grain sizes below 0.5 m. and above 5 m. up to about 20 m. are of rare occurrence. As the oxidizing agents lead dioxide and potassium perchlorate have proved good, when added to the primer in fine distribution in amount up to 35% by weight. As the binder, polyvinyl alcohol is quite suitable used in amounts of 0.4 to 4% by weight, preferably to 2% by weight, of the ignition mass. However, many other binders with similar dielectric properties may also be used. The composition of the primer corresponds to usual primers for DC. ignition. 1

The oxygen carrier or oxidizing agent may also be omitted completely; but then it is necessary that the primer shall be in an oxygen atmosphere when flashingoff so that gaseous oxygen is enclosed in the primer. Also in the presence of a solid oxidation means in the primer mass, the oxygen atmosphere supports the flashing of the primer.

For flashing-off, the primer voltage impulses of about 100 volts or more are suitable. With voltages of below about 70 volts an absolutely certain ignition cannot be obtained. The energy required for flashing is very low and amounts to about 0.3 mw. sec. (milliwatt seconds). The required voltage impulses are produced in the secondary winding of a sub-miniature transformer in such a manner that a condenser is discharged across the primary winding of this transformer. A charge on the condenser of, say, 30 [.Lf. is applied through a resistance from a battery supplying, for instance, 4.5 volts.

In the accompanying drawing, forming part hereof,

FIGURE 1 shows a longitudinal section through a photoflash lamp according to the invention; and

FIGURE 2 shows the electrical circuit in a flash gun for flashing the lamp according to the invention.

In the specific embodiment of the invention illustrated in said drawing, very much enlarged from actual size of the miniature photoflash lamp represented, is an example of a lamp comprising an envelope 1, shown as a nearly tubular glass bulb, filled with zirconium foil 2 and oxygen under pressure of, for instance, 7000mm. Hg. In the fabrication process, one end of the bulb is preclosed and the other end initially open but subsequently sealed closed by a stern flare 3. Sealed in concentrically in said flare 3 there is a copper exhaust tube 4 which also serves as what will be termed herein, for convenience, the first in-lead for the electrical current. Eccentrically in said flare 3 and paralleling the first in-lead 4, is a sealedin dumet wire constituting a second in-lead 5 for the current. These in-leads 4 and 5 are suitably spaced apart a distance within the range of 0.1 to 0.5 mm., preferably about 0.2 mm.

According to the invention, both of the current inleads 4 and 5 are bridged through a primer 6 in contact with the surfaces of both of said in-leacls. The primer 6 is composed of a mechanical mixture of finely divided zirconium powder, of above-described grain size, lead dioxide up to 35% by weight and about 2% by weight of polyvinyl alcohol. Potassium perchlorate may be substituted for or included with the lead dioxide. The polyvinyl alcohol functions as a binder. For preparing the ignition mass or primer 6, the binder is dissolved in a sol-- vent, for example, amyl acetate, and the zirconium pow-- der is suspended together with the oxidation compound, namely, the lead dioxide and/ or potassium perchlorate, in that binder solution. The mixture attains a viscous condition comparable to that of fresh putty. I

In manufacture of the lamp, both of the current in-leads 4 and 5 are sealed in flare 3 and then the upper end of the eccentric in-lead 5 is temporarily pressed laterally against the exhaust tube first in-lead 4. Due to the clasticity of the dumet wire constituting said eccentric inlead, the desired distance of about 0.2 mm. of spacing between the in-leads is obtained upon release of the lateral pressure. Thereafter the ignition mass or primer 6 is applied to the current in-leads and by virtue of the vis cosity of said mass it may be caused to adhere to said in-leads and thereby form a bridge of ignition mass across both of the current in-lead ends within the envelope. Thereafter the ignition mass or primer 6 is dried by evaporation of the solvent. After the bridge of ignition mass 6 is in place, the flare is inserted into and closes the previously open end of the envelope. It is best, before ap plying the Hare in place, to blow compressed air through the tube 4 to make certain that it is clear and not inadvertently stopped-up with any of the ignition mass or primer material. Of course the envelope is filled with the zirconium foil 2 before the stern flare is applied. After the stem flare has been scaled to complete the envelope, oxygen is introduced through the exhaust tube 4 which is then sealed-off by pinching or otherwise, and serves thereafter as the current in-lead. Where theexhaust tube is pinched, the seal may be made doubly secure by applying a solder tip 7 thereat.

A usual battery-condenser connection as part of an electrical circuit that also includes an impulse trans former and a control switch is used advantageously ac cording to the present invention for the purpose of ignit ing the lamp. As shown, a battery 8 charges a condenser 11 through a current-limiting resistance 9 rated, for instance at 5 kilohms, in series with a charging currentbreaking switch 10. The camera contact is indicated by a switch 12, and since the condenser 11 is connected into the line between the camera (switch 12) and control switch 10, when the camera switch 12 is ciosed, condenser 11 discharges across the primary winding 13 of the impulse transformer. The secondary winding 14 of that transformer has many more turns than the primary winding 13, obtaining a free-damped oscillation. In dimensioning the circuit elements, attention has been paid to the fact that space and energy requirements of the arrangement should be minimal with due regard for greatest certainty of ignition. A sub-miniature transformer is used, and said transformer is one having a ferrite head core and having a transformation ratio of 1:200 and dimensions of 9.5 x 6 mm. Preferably three turns are used for the primary winding 13 and six hundred turns for the secondary Winding 14. The primary winding consists of copper wire of 0.2 mm. diameter and the secondary Winding is copper wire of 0.05 mm. diameter. All of the elements may easily be located in a synthetic casing the dimensions of which are 40 mm. x 20 mm. x 20 mm.

The electric energy required for ignition is unexpectedly low. The battery 8 consists preferably of three monocells in series together providing 4.5 volts, and the condenser is of chosen size with about 30 ,uf. capacity. Energy required by the present invention is only about 0.3 mw. sec. (milliwatt second) in contrast to prior art requirements of 20 to 30 mw. sec. Due to the relatively high voltage involved, one end of the primary winding 13 of the transformer is preferably connected electrically to the corresponding end of the secondary 14 by grounding both or by directly connecting the same, bridge 17 shown indicating the common grounding or connection.

Observation may also be made that control switch is arranged in the flash gun in such a manner that it closes when a lamp is inserted and opens again when the lamp is removed and may be coupled with the lamp ejector. By the resultant interruption of the charging current when the flash device is not in operation, premature discharge of the battery is prevented. SwitchlZ is closed when the camera shutter is opened, as usual with flash devices. Terminals 15 and 16 are indicative of the two contacts to the flash lamp.

We claim:

1. A photoflash lamp comprising a hermetically sealed envelope filled with finely shredded combustion material and oxygen, two current in-leads the surfaces of both whereof are fully conductive electrically extending into the envelope, and an ignition mass constituting a primer applied to said electrically conductive surfaces of the current in-leads, said primer comprising finely divided easily ignitable metal particles with a dielectric binder, said primer being in direct contact with the electrically conductive surfaces of both of said current in-leads, and the electrical resistance of the primer amounting to at least one megohm under a potential of up to twenty volts, said metal particles being sufliciently close together so that at a potential of 70 volts sparking occurs therebetween and instigates flashing of the lamp.

2. A photofiash lamp as claimed in claim 1, characterized in that the primer comprises zirconium powder with grain sizes of substantially between 0.5 ,um. and 5 m. and therewith 0.4 to 4% by weight of polyvinyl alcohol as a binder.

3. A photoflash lamp as claimed in claim 2, characterized in that the primer contains up to by weight of an oxidizing agent.

4. A photoflash lamp as claimed in claim 3, characterized in that the oxidizing agent is at least in part lead oxide.

5. A photoflash lamp as claimed in claim 3, characterized in that the oxidizing agent is at least in part potassium perchlorate.

References Cited by the Examiner UNITED STATES PATENTS 2,771,765 11/1956 Arnott et al. 67-31 JAMES W. WESTHAVER, Primary Examiner. 

1. A PHOTOFLASH LAMP COMPRISING A HERMETICALLY SEALED ENVELOPE FILLED WITH FINELY SHREDDED COMBUSTION MATERIAL AND OXYGEN, TWO CURRENT IN-LEADS THE SURFACES OF BOTH WHEREOF ARE FULLY CONDUCTIVE ELECTRICALLY EXTENDING INTO THE ENVELOPE, AND AN IGNITION MASS CONSTITUTING A PRIMER APPLIED TO SAID ELECTRICALLY CONDUCTIVE SURFACES OF THE CURRENT IN-LEADS, SAID PRIMER COMPRISING FINELY DIVIDED EASILY IGNITABLE METAL PARTICLES WITH A DIELECTRIC BINDER, SAID PRIMER BEING IN DIRECT CONTACT WITH THE ELECTRICALLY CONDUCTIVE SURFACES OF BOTH OF SAID CURRENT IN-LEADS, AND THE ELECTRICAL RESISTANCE OF THE PRIMER AMOUNTING TO AT LEAST ONE MEGOHM UNDER A POTENTIAL OF UP TO TWENTY VOLTS, SAID METAL PARTICLES BEING SUFFICIENTLY CLOSE TOGETHER SO THAT AT A POTENTIAL OF 70 VOLTS SPARKLING OCCURS THEREBETWEEN AND INSTIGATES FLASHING OF THE LAMP. 